1. Field of the Invention
The present invention relates to a pressure sensor for mounting in the distal end portion of a lead or catheter intended to be placed in a living organism, such as the heart of a human being, of the type having a piezoelectric element delivering an electric signal when subjected to a pressure variation.
2. Description of the Prior Art
With the aid of a pressure sensor in the heart, tachycardias, such as fibrillation, can be detected and distinguished. Atrial fibrillation e.g. can be separated from ventricular fibrillation and electrical activity can be separated from mechanical activity. This is of importance for controlling the type of stimulation therapy to be delivered by a heart stimulator.
From the time derivative of the blood pressure, dP/dt, an indication is obtained of the contractility of the heart, which in turn is a measure of the degree of work of the body. In H. Heynen at al. “Klinische Erfahrungen mit einem auf dem rechtsventrikulären dP/dt basierenden VVIR-Schrittmacher-system”, Herzchrittmacher, Ausgabe 13, Nr. 1, pp.34-44, 1993 rate adaptive pacing based on right ventricular dP/dtmax is described. A general problem with this kind of measurement is to avoid flow generated pressure components, and for the kind of pressure measurement described it is desirable that the sensor is sensitive to pressure variations all around the periphery of the sensor.
U.S. Pat. No. 5,271,408 discloses a pacing lead with a flow meter for measuring intravascular blood flow having piezoelectric sensors that are sensitive to pressure variations all around the periphery of the sensor. In order to function correctly, the flow meter should be centered in the flow to be measured.
None of the devices described in the above documents relate to a device for determining capture by means of pressure and none of the above documents address the problem of overgrowth that might cover the pressure sensors and that thus might affect the measurements.